1. Field of the Invention
This invention relates to an improvement in a delayed coking process.
2. Description of the Prior Art
Delayed coking is a well known process in which a hydrocarbonaceous oil is heated to a coking temperature and then passed into a coking drum to produce a vapor phase product, including normally liquid hydrocarbons, and coke. The drum is decoked by hydraulic means or by mechanical means. See Hydrocarbon Processing, September, 1980, page 153. The delayed coking process is generally conducted at a temperature ranging from about 800.degree. to about 950.degree. F. Typically, delayed coking is conducted at conditions, including a temperature above about 900.degree. F., such that the coke product comprises from about 6 to about 12% volatile matter. When the content of volatile matter is below about 6 wt.%, the coke is harder and more difficult to remove from the drum. It has also been stated in the prior art that an increase in coking temperature decreases coke production and increases liquid hydrocarbon yield. The observed decrease in coke product, however, is relative to coke production at a lower temperature in which the coke contains a greater amount of volatile matter. Thus, if the coke production were to be compared on a volatile matter free basis, it would be seen that higher temperature operation produced more coke.
U.S. Pat. No. 4,036,736 discloses a delayed coking process to produce a synthetic coking coal and low sulfur fuel oil. The gaseous and liquid products from the coker are removed at accelerated velocity induced by the flow of inert gas or hydrocarbon gas. Volatile matter of the coke product is above 20 weight percent.
U.S. Pat. No. 3,956,101 discloses introducing an inert gas into a coking drum during the coking operation. The gas may be hydrogen, nitrogen, steam and hydrocarbon gases. The feed is heated in a two-step operation to produce a desired quality coke.
It has now been found that delayed coking can be conducted at a relatively low temperature while producing a coke having the desired content of volatile matter by introducing a specified amount of gas into the coking drum.